might_sleep 分析

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本文详细介绍了Linux内核中的might_sleep()宏，它用于检测在不应发生睡眠的地方是否发生了睡眠，并在发生时打印调用堆栈。该宏在CONFIG_DEBUG_ATOMIC_SLEEP配置下启用，有助于早期发现并解决潜在的原子上下文睡眠问题。

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might_sleep()用于调试在不预期睡眠的地方是否会正的睡眠
#ifdef CONFIG_PREEMPT_VOLUNTARY
extern int _cond_resched(void);
# define might_resched() _cond_resched()
#else
# define might_resched() do { } while (0)
#endif

#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
  void ___might_sleep(const char *file, int line, int preempt_offset);
  void __might_sleep(const char *file, int line, int preempt_offset);
/**
 * might_sleep - annotation for functions that can sleep
 *
 * this macro will print a stack trace if it is executed in an atomic
 * context (spinlock, irq-handler, ...).
 *
 * This is a useful debugging help to be able to catch problems early and not
 * be bitten later when the calling function happens to sleep when it is not
 * supposed to.
 */
# define might_sleep() \
	do { __might_sleep(__FILE__, __LINE__, 0); might_resched(); } while (0)
# define sched_annotate_sleep()	(current->task_state_change = 0)
#else
  static inline void ___might_sleep(const char *file, int line,
				   int preempt_offset) { }
  static inline void __might_sleep(const char *file, int line,
				   int preempt_offset) { }
# define might_sleep() do { might_resched(); } while (0)
# define sched_annotate_sleep() do { } while (0)
#endif
可以看到如果没有定义CONFIG_DEBUG_ATOMIC_SLEEP的话，might_sleep就是一个空函数，所以平常看code的时候可以忽略。
如果定义的CONFIG_DEBUG_ATOMIC_SLEEP的话，如果在包含might_sleep的函数中睡眠了，则会打印当前的callstack，具体分析如下：
void __might_sleep(const char *file, int line, int preempt_offset)
{
	/*
	 * Blocking primitives will set (and therefore destroy) current->state,
	 * since we will exit with TASK_RUNNING make sure we enter with it,
	 * otherwise we will destroy state.
	 */
//首先打印警告印象
	WARN_ONCE(current->state != TASK_RUNNING && current->task_state_change,
			"do not call blocking ops when !TASK_RUNNING; "
			"state=%lx set at [<%p>] %pS\n",
			current->state,
			(void *)current->task_state_change,
			(void *)current->task_state_change);
//继续调用___might_sleep
	___might_sleep(file, line, preempt_offset);
}
void ___might_sleep(const char *file, int line, int preempt_offset)
{
	
//调用dump_stack 打印callstack
	dump_stack();
	add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
}